Cell phone systems include base stations, or cell sites that control the output of cell phones. The control is such that if the cell phone is far from the nearest cell site the cell phone is directed to transmit at a high maximum amplitude, and so if the cell phone is close to the cell site the cell phone is directed to transmit at only a much lower maximum amplitude. TIA-98-E standards for the cell phone industry specify that maximum cell phone output cannot exceed +30 dBm (decibels above one milliwatt) even when the cell phone is far from the nearest cell site. Also, when the cell phone is near the cell site, the cell phone output cannot exceed −50 dBm (decibel below one milliwatt). The cell site controls cell phone output to comply with these standards.
Boosters are available to amplify weak signals received from a cell site and to amplify the outputs of cell phones, when the cell site is far and the received signal is weak. Such boosters commonly use a system wherein the amplifier gain is continually variable, so when the received signal is strong the amplification is low and when the received signal is very weak the amplification is high, with the power output to the antenna always kept below the limit set by the cell site. One problem with such boosters is that continuously variable amplification increases non-linear response and results in emissions, adjacent channel interference, intermodulation and desensitization. Such boosters often satisfy unknowlegeable customers, who connect a cell phone through the amplifier and measure how much the signal strength increases (as seen on the cell phone received signal strength indicator). Such unknowlegeable customers do not realize that at low levels, the noise figure of the amplifier is the primary factor that determines sensitivity. Most available boosters transmit excessive power when close to a cell site, which severely disrupts proper cell site operation.
A cell phone booster that provided maximum allowed cell phone transmission power output to a distant cell site, and maximum allowed output when close to a cell site to assure recognition, all while keeping transmitted signals within the limits set at every moment by the cell site, would be of value.